Working Machine

ABSTRACT

In a specific state where the raising operation of a boom 25 and the swing operation of an upperstructure 21 are performed at the same time to supply a hydraulic oil from a first pump 2 to a cylinder 7a through a first valve 6a, and to supply the same from a second pump 3 to a motor 7b through a second valve 6b, a controller 10 outputs the command current for opening a valve 13, and supplies a part of the hydraulic oil supplied to the motor 7b from the second pump 3 to the cylinder 7a through the third valve 6c when the motor 7b does not reach a steady swing state, and outputs a command current for closing the valve 13 when the motor 7b is in the steady swing state.

TECHNICAL FIELD

The present invention relates to a hydraulic drive technology of aworking machine such as a hydraulic excavator provided with a frontworking device.

BACKGROUND ART

In a working machine provided with a front working device, there is ahydraulic drive device for supplying a sufficient amount of hydraulicoil to a boom cylinder while inhibiting a wasteful consumption of energywhen a boom raising operation and a swing operation are performed at thesame time. For example, Patent Literature 1 discloses a hydraulic drivedevice for a working machine “which includes a first hydraulic pump anda second hydraulic pump whose tilting angles can be adjusted independentof each other, a swing control valve for controlling the supply of ahydraulic oil to a swing motor, and a boom main control valve and a boomauxiliary control valve for controlling the supply of the hydraulic oilto a boom cylinder, and the swing control valve and the boom auxiliarycontrol valve are disposed on a first bleed line, the boom main controlvalve is disposed on a second bleed line. A pilot pressure is output toswing control valve from the swing control valve, and the pilot pressureis output to the boom main control valve from the boom control valve.When the swing operation and the boom raising operation are performed atthe same time, the boom side control valve does not output the pilotpressure to the boom auxiliary control valve (abstract excerpt).”

CITATION LIST Patent Literature

-   PATENT LITERATURE 1: Japanese Patent Application Laid-Open    Publication No. 2015-86959

SUMMARY OF INVENTION Technical Problem

According to the technology disclosed in Patent Literature 1, when theboom raising operation and the swing operation are performed at the sametime, the boom auxiliary control valve shuts off the supply line of thehydraulic oil from the boom auxiliary control valve to the boomcylinder. One of the hydraulic pumps is dedicated to the swing motor,and the other hydraulic pump is dedicated to the boom cylinder, and eachhydraulic pump is controlled independently. As a result, a variablethrottle for limiting the hydraulic oil to be supplied to the swingmotor becomes unnecessary, and an energy loss of the hydraulic oilgenerated by throttling the opening of the variable throttle when aswing motor load pressure is smaller than a boom cylinder load pressurecan be reduced.

However, even when the boom raising operation and the swing operationare performed at the same time, a large force is required for swing atthe time of starting the swing, and a swing motor load pressure becomeshigher than the boom cylinder load pressure. In the technology disclosedin Patent Literature 1, even under such a condition, as long as both theoperations are being performed at the same time, the supply line to theswing motor and the supply line for the boom cylinder are independent ofeach other, so that the high swing motor load pressure may activate theswing relief valve. When the swing relief valve operates, the hydraulicoil supplied from the pump through the supply line to the swing motor isdiscarded to the hydraulic oil tank, which is wasteful.

The present invention has been made in view of the above circumstances,and an object of the present invention is to provide a technique ofeffectively leveraging an energy regardless of timing when a swingoperation and a boom raising operation are performed at the same time ina working machine provided with a front working device.

Solution to Problem

According to the present invention, there is provided a working machineincluding: a travel base, an upperstructure that is swingably mounted onthe travel base, a swing motor that drives the upperstructure, a boomthat is provided in the upperstructure to be rotatable in a verticaldirection, a boom cylinder that drives the boom, a hydraulic drivedevice that drives the swing motor and the boom cylinder, and acontroller that controls the hydraulic drive device, in which thehydraulic drive device includes: a first hydraulic pump that suppliesthe hydraulic oil to the boom cylinder; a second hydraulic pump thatsupplies the hydraulic oil to the swing motor; a boom operating devicethat outputs a boom operating pressure which is a signal for operatingthe boom; a swing operating device that outputs a swing operatingpressure which is a signal for operating the upperstructure; a firstcontrol valve that is disposed between the first hydraulic pump and theboom cylinder, and operates according to the boom operation to control adirection and a flow rate of the hydraulic oil supplied from the firsthydraulic pump to the boom cylinder; a second control valve that isdisposed between the second hydraulic pump and the swing motor andoperates according to the swing operating pressure to control thedirection and the flow rate of the hydraulic oil supplied from thesecond hydraulic pump to the swing motor; a third control valve that isdisposed between the second hydraulic pump and the boom cylinder inparallel to the second control valve, and shuts off the supply of thehydraulic oil to the boom cylinder from the second hydraulic pump andoperates according to the boom operating pressure to control thedirection and the flow rate of the hydraulic oil supplied to the boomcylinder from the second hydraulic pump, in a state where the boomoperating pressure is not introduced; an on-off solenoid valve which isdisposed between the boom operating device and the third control valveand opens and closes based on a command current from the controller; anda relief valve that is provided between the second hydraulic pump andthe swing motor, and in a specific state in which the boom raisingoperation and the swing operation of the upperstructure are performed atthe same time to supply the hydraulic oil from the first hydraulic pumpto the boom cylinder through the first control valve, and to supply thehydraulic oil from the second hydraulic pump to the swing motor throughthe second control valve, the controller outputs the command current foropening the on-off solenoid valve for introducing the boom operatingpressure to the third control valve, supplies a part of the hydraulicoil supplied to the swing motor from the second hydraulic pump to theboom cylinder through the third control valve in case it isdiscriminated that the swing motor does not reach a steady swing state,and the controller outputs the command current for closing the on-offsolenoid valve for limiting introduction of the boom operating pressureinto the third control valve in case where it is discriminated that theswing motor is in the steady swing state.

Advantageous Effects of Invention

According to the present invention, in a working machine provided with afront working device, an energy can be efficiently used regardless oftiming when the swing operation and the boom raising operation areperformed at the same time. In addition, the problems, configurationsand effects except for those described above will be clarified bydescription of the following embodiment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a hydraulic excavator according to a firstembodiment.

FIG. 2 is a block diagram of a hydraulic drive device according to thefirst embodiment.

FIG. 3 is a flowchart of a cut valve control process according to thefirst embodiment.

FIG. 4 is an illustrative view illustrating the operation of thehydraulic drive device according the first embodiment.

FIG. 5 is an illustrative view illustrating the operation of thehydraulic drive device according to the first embodiment.

FIG. 6 is a graph of temporal changes in delivery pressure of eachhydraulic pump when a boom operating pressure cut valve is shut offregardless of a load pressure at the time of a swing boom raisingoperation.

FIG. 7 is a graph of a temporal change in the delivery pressure of eachhydraulic pump according to the first embodiment.

FIG. 8 is a block diagram of a hydraulic drive device according to asecond embodiment.

FIG. 9 is a flowchart of a cut valve control process according to thesecond embodiment.

FIG. 10 is a flowchart of a cut valve control process according to amodification of the embodiment of the present invention.

FIG. 11 is a graph of a metering characteristic of a boom operatingpressure cut valve according to Modification 2 of the embodiment of thepresent invention.

FIG. 12 is a configuration diagram of a hydraulic drive device accordingto Modification 3 of the embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the embodiments of the present invention will be describedwith reference to the drawings. In each of the following embodiments, ahydraulic excavator will be described as an example of a working machinedriven by a hydraulic drive device.

First Embodiment

In the present embodiment, in a hydraulic drive device for a hydraulicexcavator including a first hydraulic pump and a second hydraulic pump,when a boom raising operation and a swing operation are performed at thesame time, the independence and non-independence of both those pumps arecontrolled taking the magnitude of a load pressure of actuators for boththe operations into consideration.

Specifically, for example, as in a swing start, when a load pressure ofthe swing motor is larger than a load pressure of the boom raisingoperation, both those pumps are made independent of each other. On theother hand, in a state where a predetermined time elapses from the swingstart, and a large force for swing is not required, both the pumps aremade independent of each other.

Hereinafter, a state in which the boom raising operation and the swingoperation are simultaneously performed is referred to as a swing boomraising operation.

First, an overview of the hydraulic excavator according to the presentembodiment will be described. FIG. 1 is a side view of a hydraulicexcavator 50 according to the present embodiment.

As shown in the figure, the hydraulic excavator 50 according to thepresent embodiment includes a travel base 20, an upperstructure 21swingably mounted on the travel base 20, a swing motor 7 b for drivingthe upperstructure 21, a front working device 22 liftably connected tothe upperstructure 21, a cab 30 provided at the front of theupperstructure 21 and a driving source chamber 31 provided at the rearof the upperstructure 21.

The front working device 22 includes a boom 25 connected to theupperstructure 21, a boom cylinder 7 a for driving the boom 25, an arm26 connected to a tip of the boom 25, an arm cylinder 28 for driving thearm, a bucket 27 connected to a tip of the arm 26, and a bucket cylinder29 for driving the bucket 27.

Each of the swing motor 7 b, the boom cylinder 7 a, the arm cylinder 28,and the bucket cylinder 29 is a hydraulic actuator that operates by ahydraulic oil supplied from a hydraulic pump to be described later.

Moreover, the hydraulic excavator 50 is provided with a hydraulic drivedevice which drives those hydraulic actuators, and a controller whichcontrols the hydraulic drive device. The hydraulic drive device and thecontroller are disposed, for example, in the driving source chamber 31.The hydraulic drive device and the controller will be described later.

A pair of travel bases 20 is provided on the left and right. Each of theleft and right travel bases 20 includes a traveling motor 23 and acrawler 24. In this example, only one travel base is illustrated. Thecrawler 24 is driven by the traveling motor 23 to cause the hydraulicexcavator 50 to travel.

[Hydraulic Drive Circuit]

Next, the hydraulic drive device 60 according to the present embodimentwill be described. FIG. 2 is a block diagram of the hydraulic drivedevice 60 according to the present embodiment.

As described above, in the present embodiment, the hydraulic drivedevice 60 is provided which efficiently use an energy when the swingoperation by the swing motor 7 b and the boom raising operation by theboom cylinder 7 a are performed at the same time. For that reason, inthis example, the swing motor 7 b and the boom cylinder 7 a are shown asthe hydraulic actuators.

The hydraulic drive device 60 includes a prime mover (for example, anengine) 1, a first hydraulic pump 2, a second hydraulic pump 3, and apilot pump 4, which are driven by the prime mover 1, and a controller 10that controls the respective devices in the hydraulic drive device 60.

The first hydraulic pump 2 supplies the hydraulic oil to the boomcylinder 7 a. The second hydraulic pump 3 mainly supplies the hydraulicoil to the swing motor 7 b.

The first hydraulic pump 2 and the second hydraulic pump 3 are swashplate type or inclined shaft type variable displacement hydraulic pumps.The first hydraulic pump 2 includes a first regulator 12 a that adjustsa tilting angle of the swash plate or the inclined shaft of the firsthydraulic pump 2. Similarly, the second hydraulic pump 3 includes asecond regulator 12 b that adjusts the same tilting angle.

Further, the hydraulic drive device 60 includes a boom operating device8 a which outputs a boom operating pressure which is a signal foroperating the boom 25 and a swing operating device 8 b which outputs aswing operating pressure which is a signal for operating theupperstructure 21.

The boom operating device 8 a and the swing operating device 8 b includecontrol levers 81 a and 81 b for receiving a boom operation by anoperator, and control valves 82 a and 82 b for outputting a boomoperating pressure according to a manipulated variable by the controllevers 81 a and 81 b, respectively.

The control levers 81 a and 81 b are provided in the cab 30. The controlvalves 82 a and 82 b are connected to the pilot pump 4, use a deliverypressure of the pilot pump 4 as an original pressure, and generate andoutput an operating pressure corresponding to the manipulated variableas a boom operating pressure and a swing operating pressure.

Further, the hydraulic drive device 60 includes a first control valve 6a, a second control valve 6 b and a third control valve 6 c whichcontrol a direction and a flow rate of the hydraulic oil, a boomoperating pressure cut valve 13 which is an on-off solenoid valve thatopens and closes based on a command current from the controller 10, anda swing relief valve 14 that protects a supply path of the hydraulic oilto the swing motor 7 b from an excessive pressure.

The first control valve 6 a is disposed between the first hydraulic pump2 and the boom cylinder 7 a, and operates according to the boomoperating pressure, and controls the direction and the flow rate of thehydraulic oil supplied from the first hydraulic pump 2 to the boomcylinder 7 a.

The second control valve 6 b is disposed between the second hydraulicpump 3 and the swing motor 7 b, and operates according to the swingoperating pressure, and controls the direction and the flow rate of thehydraulic oil supplied from the second hydraulic pump 3 to the swingmotor 7 b.

The third control valve 6 c is provided between the second hydraulicpump 3 and the boom cylinder 7 a in parallel to the second control valve6 b. Then, the third control valve 6 c operates according to the boomoperating pressure to control the direction and flow rate of thehydraulic oil supplied from the second hydraulic pump 3 to the boomcylinder 7 a. The third control valve 6 c shuts off the supply of thehydraulic oil from the second hydraulic pump 3 to the boom cylinder 7 awhen the boom operating pressure is not introduced.

The boom operating pressure cut valve 13 is disposed between the boomoperating device 8 a and the third control valve 6 c, and restricts theboom operating pressure based on a command current from the controller.

The swing relief valve 14 is provided between the second hydraulic pump3 and the swing motor 7 b to protect the supply path of the hydraulicoil to the swing motor 7 b from an excessive pressure. The swing reliefvalve 14 operates when reaching a set pressure (set pressure), opens acircuit leading to the hydraulic oil tank 5, allows the hydraulic oil inthe circuit to flow into the hydraulic oil tank 5, and reduces apressure in the circuit.

The controller 10 receives each sensor signal and controls each part ofthe hydraulic excavator 50. In the present embodiment, a cut valvecontrol process is performed to control the opening and closing of theboom operating pressure cut valve 13 according to the operating pressureand the load pressure. For example, the controller 10 receives a boomoperating pressure from the boom operating pressure sensor 9 a, theswing operating pressure from the swing operating pressure sensor 9 b,the boom load pressure from the boom cylinder pressure sensor 11 a, andthe swing load pressure from the swing motor pressure sensor 11 b, andwhen a predetermined condition is satisfied, the controller 10 outputs aclose command to the boom operating pressure cut valve 13.

Specifically, at the time of the swing boom raising operation, in aspecific state in which the hydraulic oil is supplied from the firsthydraulic pump 2 to the boom cylinder 7 a through the first controlvalve 6 a, and the hydraulic oil is supplied from the second hydraulicpump 3 to the swing motor 7 b through the second control valve 6 b, ifthe swing load pressure is equal to or higher than the boom loadpressure, the controller 10 outputs a command current so as to open theboom operating pressure cut valve 13 in order to introduce the boomoperating pressure to the third control valve 6 c. As a result, thecontroller 10 supplies a part of the hydraulic oil supplied from thesecond hydraulic pump 3 to the swing motor 7 b to the boom cylinder 7 athrough the third control valve 6 c. On the other hand, when the swingload pressure is smaller than the boom load pressure, the controller 10outputs the command current so as to close the boom operating pressurecut valve 13 in order to restrict the introduction of the boom operatingpressure to the third control valve 6 c.

Hereinafter, in the present embodiment, the command current to be outputto open the boom operating pressure cut valve 13 is called “opencommand”, and the command current to be output to close the boomoperating pressure cut valve 13 is called “close command”. In thepresent embodiment, a current value of the open command is set to 0. Inother words, when no current is output, the boom operating pressure cutvalve 13 passes the boom operating pressure as it is, and shuts off theboom operating pressure when a closing command is received.

The controller 10 is realized by an arithmetic device including acentral processing unit (CPU), a random access memory (RAM), and astorage device such as a read only memory (ROM) or a hard disk drive(HDD).

In the cut valve control process, the controller 10 first determineswhether or not the swing motor 7 b is in the swing boom raisingoperation, based on whether or not the boom operating pressure and theswing operating pressure are received. When it is determined that theswing motor 7 b is in the swing boom raising operation, the controller10 determines whether the operation is immediately after the start ofthe swing boom raising operation or the second half of the operation.When it is determined that the operation is in the second half of theoperation, the controller 10 outputs a command (close command) forclosing the valve to the boom operating pressure cut valve 13.

Immediately after the start of the swing boom raising operation, asdescribed above, a large force is required to start the swing motor 7 b.On the other hand, during the second half of operation, a large force isnot required for the swing motor 7 b. A state of the swing motor 7 bwhen the large force at the second half of the operation is no longerrequired is referred to as “a steady swing state”. In the presentembodiment, the magnitudes of the boom load pressure and the swing loadpressure are compared with each other, and when the boom load pressureis larger than the swing load pressure, it is assumed that the swingmotor 7 b is in the steady swing state.

Hereinafter, a flow of the cut valve control process by the controller10 will be described according to a flow of FIG. 3. The cut valvecontrol process is performed at predetermined time intervals. Further,before the start of processing, the boom operating pressure cut valve 13is in an open state.

First, the controller 10 determines whether or not the swing operationhas been performed (Step S1101). As described above, when the swingoperating pressure is received from the swing operating pressure sensor9 b, the controller 10 determines that the swing operation has beenperformed. Then, when it is not determined that the swing operation hasbeen performed, the process is completed.

If it is determined that the swing operation has been performed, thecontroller 10 determines whether or not the boom operation has beenperformed (Step S1102). As described above, when the boom operatingpressure is received from the boom operating pressure sensor 9 a, thecontroller 10 determines that the boom operation has been performed.Then, if it is not determined that the boom operation has beenperformed, the processing is completed.

If it is determined that the boom operation has been performed, thecontroller 10 compares the boom load pressure with the swing loadpressure (Step S1103).

As a result of comparison, when the boom load pressure is larger thanthe swing load pressure, the controller 10 outputs the close command tothe boom operating pressure cut valve 13 (Step S1104), and the processis ended. The controller 10 is configured to discriminate that the swingmotor 7 b is in the steady swing state when the boom load pressure islarger than the swing load pressure.

On the other hand, when the boom load pressure is equal to or less thanthe swing load pressure, the process is completed as it is. In thatcase, the controller 10 determines that the swing motor 7 b is at thestart of swing where a large load is applied to the swing motor 7 b andthat the swing motor 7 b does not reach the steady swing state.

Note that either of Steps S1101 and S1102 may be performed first.

Next, the operation of the hydraulic drive device 60 according to thepresent embodiment when the above control is performed will be describedwith reference to FIGS. 4 and 5. In the figure, lines through which thehydraulic oil flows are indicated by thick lines. Moreover, linesthrough which the pilot pressure oil flows due to the operating pressureare indicated by alternate long and short dash lines.

As shown in the figure, at the time of the boom raising operation, aboom raising operating pressure da is generated by operating the controllever 81 a (the boom operating device 8 a) in a right direction in thefigure. Due to the boom raising operating pressure da, the first controlvalve 6 a strokes from a neutral position to the right in the figure,and the hydraulic oil of the first hydraulic pump 2 flows into thebottom side of the boom cylinder 7 a.

Further, at the time of the swing operation, a swing operating pressuredb (swing operating device 8 b) is generated by operating the controllever 81 b (swing operating device 8 b) in a first direction. With theswing operating pressure db, the second control valve 6 b strokes to theright in the drawing, and the hydraulic oil of the second hydraulic pump3 is supplied to the swing motor 7 b and returns to the hydraulic oiltank 5 through the second control valve 6 b.

Upon detecting the boom raising operating pressure da, the boomoperating pressure sensor 9 a outputs the detected boom raisingoperating pressure da to the controller 10. In the same manner, upondetecting the swing operating pressure db, the swing operating pressuresensor 9 b outputs the detected swing operating pressure db to thecontroller 10. Further, the boom cylinder pressure sensor 11 a detects aboom load pressure Pa, and the swing motor pressure sensor 11 b detectsa swing load pressure Pb, and those sensors 11 a and 11 b output thedetected load pressures to the controller 10.

At the start of the swing boom raising operation, as described above,the swing load pressure Pb is equal to or higher than the boom loadpressure Pa (Pb≥Pa). For that reason, the controller 10 does not outputa close command cc to the boom operating pressure cut valve 13. Thus,the boom operating pressure cut valve 13 is in an open state.

Therefore, at the start of the swing boom raising operation, as shown inFIG. 4, the boom raising operating pressure da also acts on the thirdcontrol valve 6 c, and causes the third control valve 6 c to stroke tothe right in the figure. As a result, the hydraulic oil of the secondhydraulic pump 3 also flows into a bottom side of the boom cylinder 7 a.

As described above, when the swing load pressure Pb is equal to orhigher than the boom load pressure Pa, the hydraulic oil of the secondhydraulic pump 3 is supplied to both the swing motor 7 b and the boomcylinder 7 a.

At that time, the hydraulic oil delivered from the rod side returns tothe hydraulic oil tank 5 through the third control valve 6 c and thefirst control valve 6 a.

On the other hand, when the rotation of the swing motor 7 b is in asteady swing state, the swing load pressure Pb decreases and becomessmaller than the boom load pressure Pa (Pb<Pa). At that time, thecontroller 10 outputs the close command cc to the boom operatingpressure cut valve 13 as shown in FIG. 5.

As shown in the figure, when the close command cc is output, the boomoperating pressure cut valve 13 shuts off the boom raising operatingpressure da acting on the third control valve 6 c. As a result, thethird control valve 6 c does not stroke and is in a neutral state. Forthat reason, the hydraulic oil from the second hydraulic pump 3 is notsupplied to the boom cylinder 7 a.

At that time, as in FIG. 4, the boom raising operating pressure da actson the first control valve 6 a to lead the hydraulic oil of the firsthydraulic pump 2 to the cylinder bottom side of the boom cylinder 7 a.Further, the swing operating pressure db acts on the second controlvalve 6 b, and leads the hydraulic oil of the second hydraulic pump 3 tothe swing motor 7 b.

This makes it possible to realize an independent circuit in which thefirst hydraulic pump 2 is dedicated to the boom cylinder 7 a and thesecond hydraulic pump 3 is dedicated to the swing motor 7 b. In thisway, the boom operating pressure cut valve 13 is switched, thereby beingcapable of realizing an independent circuit and a parallel circuit.

As described above, according to the present embodiment, in thehydraulic drive device 60 for the hydraulic excavator 50, the boomoperating pressure cut valve 13 is opened in order to introduce the boomoperating pressure to the third control valve 6 c to supply a part ofthe hydraulic oil to be supplied from the second hydraulic pump 3 to theswing motor 7 b to the boom cylinder 7 a through the third control valve6 c when the swing load pressure is equal to or more than the boom loadpressure, in the specific state where, at the time of the swing boomraising operation, the hydraulic oil is supplied from the firsthydraulic pump 2 to the boom cylinder 7 a through the first controlvalve 6 a, and the hydraulic oil is supplied from the second hydraulicpump 3 to the swing motor 7 b through the second control valve 6 b.Also, when the swing load pressure becomes less than the boom loadpressure, it is discriminated that the swing motor 7 b is in the steadyswing state, and the close command is output so as to close the boomoperating pressure cut valve 13 in order to restrict the introduction ofthe boom operating pressure to the third control valve 6 c.

The hydraulic excavator 50 requires a large swing force particularly atthe start of swing, because the moment of inertia of the upperstructure21 is large at the time of swing. Even when the boom raising operationand the swing operation are performed at the same time, the swing loadpressure is larger than the boom loading pressure at the start of swing.

FIG. 6 shows pressure waveforms of delivery pressures of the firsthydraulic pump 2 and the second hydraulic pump 3 when the boom operatingpressure cut valve 13 is shut off in a state where the swing loadpressure Pb is larger than the boom load pressure Pa during the swingboom raising operation. In the drawing, Pr is a set pressure of theswing relief valve 14. Also, P1 and P2 are the delivery pressures of thefirst hydraulic pump 2 and the second hydraulic pump 3, respectively.

As shown in the figure, at the start of the swing, the delivery pressureof the second hydraulic pump 3 rises to the set pressure Pr of the swingrelief valve 14. As a result, the swing relief valve 14 is opened, andthe hydraulic oil is discarded in the hydraulic tank 5, which is vain.

However, in the present embodiment, when the swing load pressure Pb isequal to or higher than the boom load pressure Pa as at the start of theswing, the boom operating pressure cut valve 13 is opened even when theswing boom raising operation is performed, and the operating pressure isled to the two control valves 6 a and 6 c. As a result, a hydraulic oilsupply line (swing line) to the swing motor 7 b and a hydraulic oilsupply line (boom line) to the boom cylinder 7 a are connected to eachother in parallel as a parallel circuit and the hydraulic oil from thesecond hydraulic pump 3 is diverted to the swing motor 7 b and the boomcylinder 7 a.

When the boom load pressure Pa becomes larger than swing load pressurePb, boom operating pressure cut valve 13 is shut off. The output of theoperating pressure to the third control valve 6 c installed on the swingline side is shut off, and the swing line and the boom line areseparated from each other as an independent circuit. As a result, thefirst hydraulic pump 2 and the second hydraulic pump 3 are used forswing only and boom only, respectively.

FIG. 7 shows the pressure waveforms of the delivery pressures of thefirst hydraulic pump 2 and the second hydraulic pump 3 at that time. Asin FIG. 6, Pa is a boom load pressure, and P1 and P2 are a deliverypressure of the first hydraulic pump 2 and a delivery pressure of thesecond hydraulic pump 3, respectively. In addition, T1 is a time whenthe boom load pressure Pa becomes larger than the swing load pressurePb.

When the boom operating pressure cut valve 13 is not shut off, that is,in the case of the parallel circuit, the pressure of the actuator isaffected by a pressure of the actuator with a lower load pressure, andall become equal in the circuit. Therefore, as shown in the figure, thedelivery pressure P1 of the first hydraulic pump 2 and the deliverypressure P2 of the second hydraulic pump 3 also have substantially thesame value. Accordingly, the hydraulic oil flowing into the hydraulicoil tank 5 by the swing relief in the independent circuit merges intothe boom cylinder 7 a. Therefore, unnecessary consumption of energy bythe swing relief is eliminated without operating the swing relief valve14.

In addition, at a time T1 transition, that is, when the boom loadpressure Pa becomes larger than the swing load pressure Pb, the boomoperating pressure cut valve 13 is shut off. As a result, the firsthydraulic pump 2 and the second hydraulic pump 3 are respectively usedfor swing only and boom only, so that the delivery pressure of each pumpcan be controlled independently. As a result, the variable throttle forsupplying the hydraulic oil into the swing motor 7 b, which is requiredif the boom load pressure is higher than the swing load pressure in theparallel circuit, is not required.

As described above, according to the present embodiment, the parallelcircuit and the independent circuit are selectively used according tothe load pressure of the actuator at the time of the swing boom raisingoperation. This makes it possible to inhibit wasteful energy consumptionin the swing relief which has occurred in the case of the independentcircuit. In addition, the shortage of hydraulic oil supply to the boomcylinder can be eliminated. The wasteful consumption of the energy dueto the passing through the variable throttle generated in the parallelcircuit is also eliminated. Therefore, the energy can be usedefficiently.

In the technique disclosed in Patent Literature 1, since only the pilotpressure is used to control the boom auxiliary control valve, it isdifficult to perform a control according to changes in the load pressureof the boom cylinder and the load pressure of the swing motor. However,according to the present embodiment, since the load pressure of the boomcylinder and the load pressure of the swing motor are used, the optimalcontrol can be performed according to the changes in those loadpressures.

Moreover, those load pressures are parameters detected by the normalhydraulic drive device 60. For that reason, according to the presentembodiment, the hydraulic drive device 60 capable of efficiently usingthe energy can be realized without adding a new configuration.

Second Embodiment

Next, a second embodiment of the present invention will be described. Inthe present embodiment, an acceleration sensor for detecting theacceleration of swing is provided. In the present embodiment, at thetime of the swing boom raising operation, whether or not the operationis at the start of the high swing load pressure is detected by theacceleration sensor.

Hereinafter, the present embodiment will be described focusing on aconfiguration different from that of the first embodiment.

A hydraulic excavator 50 which is an example of a working machineaccording to the present embodiment basically has the same configurationas that of the hydraulic excavator 50 in the first embodiment.

A hydraulic drive device 60 a according to the present embodiment isalso the same basically as the hydraulic drive device 60 of the firstembodiment. However, as shown in FIG. 8, in the present embodiment, anacceleration sensor 11 c is provided instead of the swing motor pressuresensor 11 b. The hydraulic drive device 60 a may further include a swingmotor pressure sensor 11 b. Moreover, the processing content of thecontroller 10 a according to the embodiment is also different from thatin the first embodiment.

The acceleration sensor 11 c detects an acceleration (referred to as aswing acceleration) of the swing motor 7 b at predetermined timeintervals. Each time the swing acceleration is detected, theacceleration sensor 11 c transmits the detected swing acceleration to acontroller 10.

As in the first embodiment, the controller 10 according to the presentembodiment determines whether or not the swing motor 7 b is in the swingboom raising operation by the boom operating pressure and the swingoperating pressure. When it is determined that the swing motor 7 b is inthe swing boom raising operation, the controller 10 determines whetherthe swing motor 7 b is immediately after the start of the swing boomraising operation or in a steady swing state. Then, when it isdetermined that the swing motor 7 b is in the steady swing state, thecontroller 10 outputs a close command to the boom operating pressure cutvalve 13.

Immediately after the start of the swing boom raising operation, theswing acceleration changes significantly. On the other hand, in thesteady swing state, the swing acceleration is kept substantiallyconstant. In other words, a constant speed swing is performed. Thecontroller 10 according to the present embodiment uses the aboveoperation to determine whether or not the swing motor 7 b is just afterthe start or in the steady swing state depending on whether or not theconstant speed swing is in progress. When it is determined that constantspeed swing is in progress, the controller 10 assumes that the swingmotor 7 b is in the steady swing state, and the controller 10 outputsthe close command to the boom operating pressure cut valve 13.

Specifically, when the controller 10 receives the swing accelerationfrom the acceleration sensor 11 c, the controller 10 compares thereceived swing acceleration with a value of the swing accelerationreceived one time ago. When the latest swing acceleration (most recentacceleration) is equal to the swing acceleration received one timepreviously (previous acceleration), the controller 10 determines thatthe constant speed swing is in progress. The swing acceleration receivedone time ago is stored in a RAM or the like.

Further, the determination that the constant speed swing is in progressis not limited to the case where the latest acceleration and theprevious acceleration coincide with each other. For example, when anabsolute value of a difference between those accelerations is equal toor less than a predetermined threshold, the controller 10 may determinethat the constant speed swing is in progress. In other words, if theamount of change in acceleration is within a predetermined range, thecontroller 10 may determine that constant speed swing is in progress.

Hereinafter, a flow of the cut valve control process performed by thecontroller 10 according to the present embodiment will be described withreference to a flow of FIG. 9. The same parts as those in the firstembodiment will not be described. Further, the cut valve control processof the present embodiment is also performed at predetermined timeintervals as in the first embodiment. In this example, it is assumedthat a time interval at which the cut valve control process is performedis Δt, and the current time is t.

First, as in the first embodiment, the controller 10 discriminateswhether or not the swing boom raising operation is in program inaccordance with the swing operating pressure and the boom operatingpressure (Steps S1101 and S1102). If the swing boom raising operation isnot performed, the process is ended as it is.

On the other hand, when it is determined that the swing motor 7 b is inthe swing boom raising operation, the controller 10 determines whetheror not the swing motor 7 b is in the constant speed swing operation bythe above method (Step S1203).

In Step S1203, the controller 10 compares a swing acceleration ac (t)acquired at a time t with a previously acquired swing accelerationac(t−Δt). Then, if both those accelerations are equal to each other, thecontroller 10 determines that the constant speed swing is in progress.Alternatively, if an absolute value of a difference between those swingaccelerations is less than or equal to a predetermined threshold, thecontroller 10 determines that the constant speed swing is in progress.

If the constant speed swing is not in progress, the process isterminated as it is. On the other hand, when it is determined that theswing motor 7 b is in the constant speed swing operation, the controller10 outputs a close command to the boom operating pressure cut valve 13(Step S1104), and the process is terminated.

As described above, according to the present embodiment, theacceleration sensor 11 c which detects a swing acceleration of the swingmotor 7 b and outputs the swing acceleration to the controller 10 isfurther provided. When the amount of change in the swing accelerationfalls within the predetermine range in the specific state describeabove, the controller 10 discriminates that the steady swing state is inprogress, and outputs the close command to the boom operating pressurecut valve 13.

Therefore, according to the present embodiment, as in the firstembodiment, even during the swing boom raising operation, as in the caseimmediately after the start, when a large load is applied to the swingoperation, the swing line and the boom line are connected in parallel.Then, when the swing motor 7 b becomes in the steady swing state, boththose lines are separated from each other to form an independentcircuit. For that reason, similar to the first embodiment, an energy canbe efficiently utilized.

For example, when it is determined by load pressure whether the swingmotor 7 b is immediately after the start or in the steady swing state,the load pressure of the actuator may rise under an influence ofexternal force, such as when the front working device 22 is pressedagainst a wall or ground. However, according to the present embodiment,since the acceleration of the swing motor 7 b is directly detected andthe shutoff and conduction of the boom operating pressure cut valve 13are controlled with the use of the result, the state of the swing motor7 b can be reflected on the control of the hydraulic drive device 60with high accuracy.

Modification

Note that both the swing motor pressure sensor 11 b and the accelerationsensor 11 c may be provided. A flow of the cut valve control process bythe controller 10 in that case is shown in FIG. 10.

First, similarly to the first embodiment, the controller 10 determineswhether or not the swing motor is in the swing boom raising operationbased on the swing operating pressure and the boom operating pressure(Steps S1101 and S1102). If it is determined that the swing boom raisingoperation is not in progress, the process is ended.

On the other hand, if it is determined that the swing boom raisingoperation is in progress, the controller 10 compares the boom loadpressure with the swing load pressure (Step S1103). If the boom loadpressure is equal to or less than the swing load pressure, the processis terminated.

If the boom load pressure is larger than the swing load pressure, thecontroller 10 determines whether or not a constant speed swing is inprogress (Step S1203). If the constant speed swing is not in progress,the process is terminated as it is. This determination is performed inthe same manner as in the second embodiment.

On the other hand, when it is determined that the swing motor is in theconstant speed swing operation, the controller 10 outputs the closecommand to the boom operating pressure cut valve 13 (Step S1204), andthe process is terminated.

According to the present modification, first, only when it is determinedthat the possibility of the steady swing state is high due to the loadpressure, the determination is made based on acceleration. For thatreason, it can be determined efficiently and accurately whether or notthe operation is in the steady swing state. Therefore, according to thepresent modification, a control can be performed with higher accuracy,and the energy efficiency can be further improved.

Modification 2

Further, in each of the embodiments described above, the example inwhich the on-off solenoid valve (ON-OFF valve) having only two states ofopen and close (shutoff and conduction) is used as the boom operatingpressure cut valve 13 is described. However, the boom operating pressurecut valve 13 is not limited to the above example. For example, the boomoperating pressure cut valve 13 may be configured by a spool valvehaving a metering.

FIG. 11 shows an example of a metering characteristic of the boomoperating pressure cut valve 13 according to the present modification.In the drawing, the horizontal axis is a spool stroke [mm], and thevertical axis is an opening area [mm²] of the boom operating pressurecut valve 13. As shown to the figure, the opening area of the boomoperating pressure cut valve 13 according to the present modificationmonotonously reduces with an increase of a spool stroke. The spoolstroke of the boom operating pressure cut valve 13 is determinedaccording to an integrated value of the command current of the closecommand from the controller 10.

The controller 10 according to the present modification outputs theclose command to the boom operating pressure cut valve 13 when the boomload pressure is larger than the swing load pressure. In this situation,the controller 10 continues to output the close command. As a result,the opening area of the boom operating pressure cut valve 13 becomessmall according to the characteristic of FIG. 11.

According to the present modification, the energy can be efficientlyused as in the above embodiments. Furthermore, according to the presentmodification, the boom operating pressure cut valve 13 has the meteringcharacteristic. For that reason, switching between the parallel circuitand the independent circuit can be smoothly performed.

According to the present modification, when the boom operating pressurecut valve 13 is not completely closed, the parallel circuit isconfigured. At that time, as described above, the third control valve 6c can be controlled by the boom operating pressure cut valve 13. Forthat reason, the flow rate distribution of the hydraulic oil to the boomcylinder 7 a and the swing motor 7 b in the parallel circuit mode can becontrolled by only the first control valve 6 a, the second control valve6 b, and the third control valve 6 c without changing the tilting of thepump. This enables a finer control of the flow rate.

Furthermore, in the conventional circuit, while attempting to drivemultiple actuators, since the hydraulic oil is likely to flow into theactuator lower in the load pressure, a throttle is installed on a bleedline in order to adjust a balance of the pressure. However, with the useof the boom operating pressure cut valve 13 having a metering, the boomoperating pressure cut valve 13 plays a role of the throttle. In otherwords, the third control valve 6 c is controlled with the result thatthe boom operating pressure cut valve 13 realizes the role of thethrottle. Therefore, the pressure balance can be controlled withoutproviding a throttle on the bleed line. Therefore, the wastefulconsumption of energy can be inhibited.

Modification 3

Furthermore, the spool opening degree of the boom operating pressure cutvalve 13 may be adjusted according to the temperature of the hydraulicoil.

In that case, the hydraulic drive device 60 b, as shown in FIG. 12,includes a temperature sensor 15 for detecting the temperature of thehydraulic oil. Then, the detection result of the temperature sensor 15is output to the controller 10.

The controller 10 adjusts the spool opening degree of the boom operatingpressure cut valve 13 according to the temperature of the hydraulic oil.In this example, the boom operating pressure cut valve 13 has a meteringcharacteristic shown in FIG. 11 as in Modification 2.

The viscosity of the hydraulic oil is changed with temperature asdescribed above. For that reason, a pressure loss of the hydraulic drivedevice 60 b differs depending on a difference in the temperature. Inother words, when the hydraulic oil is at a low temperature, theviscosity is high and the pressure loss of the hydraulic drive device 60b is high. Therefore, the opening degree of the boom operating pressurecut valve 13 is set to be larger so that the hydraulic oil can flow moreeasily as the temperature of the hydraulic oil is lower.

Therefore, in the present modification, the controller 10 outputs acommand to the boom operating pressure cut valve 13 to open the openingdegree of the boom operating pressure cut valve 13 more as the detectedtemperature of the hydraulic oil is lower. In this case, for example,the magnitude of the command current of the closing command to be outputis set to be smaller than that in the case of Modification 2.

As described above, the opening degree of the boom operating pressurecut valve 13 is adjusted according to the temperature of the hydraulicoil, thereby being capable of avoiding a deviation from the targetcontrol value due to a change in the pressure loss caused by the changeof the temperature. Therefore, a constant driving state can bemaintained regardless of the temperature.

REFERENCE SIGNS LIST

-   1: prime mover, 2: first hydraulic pump, 3: second hydraulic pump,    4: pilot pump, 5: hydraulic oil tank, 6 a: first control valve, 6 b:    second control valve, 6 c: third control valve, 7 a: boom cylinder,    7 b: swing motor, 8 a: boom operating device, 8 b: swing operating    device, 9 a: boom operating pressure sensor, 9 b: swing operating    pressure sensor, 10: controller, 10 a: controller, 11 a: boom    cylinder pressure sensor, 11 b: swing motor pressure sensor, 11 c:    acceleration sensor, 12 a: first regulator, 12 b: second regulator,    13: boom operating pressure cut valve, 14: swing relief valve, 15:    temperature sensor, 20: travel base, 21: upperstructure, 22: front    working device, 23: traveling motor, 24: crawler, 25: boom, 26: arm,    27: bucket, 28: arm cylinder, 29: bucket cylinder, 30: cab, 31:    motor chamber, 50: hydraulic excavator, 60: hydraulic drive device,    60 a: hydraulic drive device, 60 b: hydraulic drive device, 81 a:    control lever, 81 b: control lever, 82 a: control valve, 82 b:    control valve

1. A working machine comprising: a travel base, an upperstructure thatis swingably mounted on the travel base, a swing motor that drives theupperstructure, a boom that is provided in the upperstructure to berotatable in a vertical direction, a boom cylinder that drives the boom,a hydraulic drive device that drives the swing motor and the boomcylinder, and a controller that controls the hydraulic drive device,wherein the hydraulic drive device includes: a first hydraulic pump thatsupplies a hydraulic oil to the boom cylinder; a second hydraulic pumpthat supplies the hydraulic oil to the swing motor; a boom operatingdevice that outputs a boom operating pressure which is a signal foroperating the boom; a swing operating device that outputs a swingoperating pressure which is a signal for operating the upperstructure; afirst control valve that is disposed between the first hydraulic pumpand the boom cylinder, and operates according to the boom operatingpressure to control a direction and a flow rate of the hydraulic oilsupplied from the first hydraulic pump to the boom cylinder; a secondcontrol valve that is disposed between the second hydraulic pump and theswing motor and operates according to the swing operating pressure tocontrol the direction and the flow rate of the hydraulic oil suppliedfrom the second hydraulic pump to the swing motor; a third control valvethat is disposed between the second hydraulic pump and the boom cylinderin parallel to the second control valve, and shuts off a supply of thehydraulic oil to the boom cylinder from the second hydraulic pump andoperates according to the boom operating pressure to control thedirection and the flow rate of the hydraulic oil supplied to the boomcylinder from the second hydraulic pump, in a state where the boomoperating pressure is not introduced; an on-off solenoid valve which isdisposed between the boom operating device and the third control valveand opens and closes based on a command current from the controller; anda relief valve that is provided between the second hydraulic pump andthe swing motor, and in a specific state in which a boom raisingoperation and a swing operation of the upperstructure are performed at asame time to supply the hydraulic oil from the first hydraulic pump tothe boom cylinder through the first control valve, and to supply thehydraulic oil from the second hydraulic pump to the swing motor throughthe second control valve, the controller outputs the command current foropening the on-off solenoid valve for introducing the boom operatingpressure to the third control valve, and supplies a part of thehydraulic oil supplied to the swing motor from the second hydraulic pumpto the boom cylinder through the third control valve in case it isdiscriminated that the swing motor does not reach a steady swing state,and the controller outputs the command current for closing the on-offsolenoid valve for limiting introduction of the boom operating pressureinto the third control valve in case where it is discriminated that theswing motor is in the steady swing state.
 2. The working machineaccording to claim 1, wherein the hydraulic drive device furtherincludes: a boom cylinder pressure sensor that detects a boom loadpressure which is a load pressure of the boom cylinder and outputs theboom load pressure to the controller; and a swing motor pressure sensorthat detects a swing load pressure which is the load pressure of theswing motor and outputs the swing load pressure to the controller, andthe controller compares the boom load pressure with the swing loadpressure in the specific state, and discriminates that the swing motoris in the steady swing state in case where the boom load pressure isgreater than the swing load pressure.
 3. The working machine accordingto claim 1, wherein the hydraulic drive device further comprises anacceleration sensor that detects a swing acceleration of the swing motorand outputs the swing acceleration to the controller, and the controllerdiscriminates that the swing motor is in the steady swing state when anamount of change of swing acceleration falls within a predeterminedrange in the specific state.
 4. The working machine according to claim1, wherein the hydraulic drive device further includes: a boom cylinderpressure sensor that detects a boom load pressure which is a loadpressure of the boom cylinder and outputs the boom load pressure to thecontroller; a swing motor pressure sensor that detects a swing loadpressure which is a load pressure of the swing motor and outputs theswing load pressure to the controller; and an acceleration sensor thatdetects a swing acceleration of the swing motor and outputs the swingacceleration to the controller, and the controller discriminates thatthe swing motor is in the steady swing state in case, as a result ofcomparing the boom load pressure with the swing load pressure, the boomload pressure is larger than the swing load pressure, and an amount ofchange of the swing acceleration detected by the acceleration sensorfalls within a predetermined range in the specific state.
 5. The workingmachine according to claim 1, wherein the on-off solenoid valve has ametering characteristic in which the boom operating pressure to beconducted decreases as a spool stroke determined by an integrated valueof the command current increases from the controller.
 6. The workingmachine according to claim 5, further comprising a temperature sensorthat detects a temperature of the hydraulic oil to output the detectedtemperature to the controller, wherein the controller decreases amagnitude of the command current to be output as the temperaturedetected by the temperature sensor is lower.